CLOSE HORSE: Bobby Parnell will open the Mets’ season as the closer, and according to pitching coach Dan Warthen, will hold onto the job “if Bobby’s doing well,” no matter the health of Frank Francisco.Anthony J. Causi

CLOSE HORSE: Bobby Parnell will open the Mets’ season as the closer, and according to pitching coach Dan Warthen, will hold onto the job “if Bobby’s doing well,” no matter the health of Frank Francisco. (Anthony J. Causi)

PORT ST. LUCIE — Bobby Parnell’s stint as the Mets’ closer may not be temporary.

Manager Terry Collins tabbed Parnell to take over the spot if Frank Francisco isn’t ready to start the season in his prolonged comeback from elbow soreness, but pitching coach Dan Warthen said yesterday it will be Parnell’s job to lose.

Parnell gave up his first run of the spring yesterday in a 9-6 victory over the Astros at Tradition Field. After retiring the first two batters he faced in the ninth, he fumbled a play covering first to extend the inning and surrendered an unearned run.

“He was working on his two-seamer,” the manager said. “We all know he can throw 100 [mph], but we want him to get easy outs, because if he has to throw 25 pitches a night at 100 mph, we’re not going to be able to use him many nights in a row. And if you’re going to pitch in the back end [of the bullpen], you’ve got to be out there three out of four [games].”

It’s all part of the transition from setup man to closer, which has consistently been a rough one for Parnell, now 28.

Both Parnell and Warthen are confident the reliever finally is ready to make the leap. And they point to the end of last season, when Parnell finished a solid year with 11 1/3 straight scoreless innings in his last 11 appearances, including three saves as evidence.

“I’ve picked up where I left off,” Parnell said. “My confidence is there and I’m not really trying to find anything. It helps that I had some chances to close last year and I feel like it went well.”

Parnell, though, has expressed optimism before and not been able to follow through. Warthen thinks experience and mindset are the reasons this season could be different.

“He’s as mature as I’ve ever seen him,” Warthen said. “He’s as focused as I’ve ever seen him and as confident as I’ve ever seen him. And I think he believes he can do it, which is all that matters. I’ve always thought he could do it.”

As for the delay, Warthen said Parnell and the Mets are primed to get “a return on their investment.”

“He was a third baseman for a long time and spent three years as a starter,” Warthen said. “So there’s a different learning curve.”

Despite the vote of confidence, Parnell knows he still has something to prove, especially if Francisco recovers quickly.

“They signed him to a two-year deal,” Parnell said of Francisco’s $12 million contract. “Even if I’m closing when he’s not healthy, he’s still considered the closer. But that doesn’t affect me. I’ve been in the big leagues long enough to know the word games and things like that.”

Last week, newcomer LaTroy Hawkins said he thought the Mets were grooming Parnell to be the closer, but Parnell is doing his best to keep that out of his mind.

“I know what I have to do,” Parnell said. “If I start thinking too much, I get lost.”

That’s one of the reasons he’s found himself in trouble in the past.

“You want something so bad and you don’t know how to do it or how to get it,” Parnell said. “I’ve tried to go through the motions to psyche myself up to do it. I just need to get it done.”